modified plugin: ERROR Activity Class Schema is invalid: ,230 - start process

We have a problem in an environment with a modified plugin. The plugin is deployed well but when starting a process, which has a smartservice of that plugin, it gives the following error:

In server.log we can see this:

07:00:38,838 INFO [stdout] (http-0.0.0.0:8443-8) 423794304 [http-0.0.0.0:8443-8] ERROR com.appiancorp.process.runtime.processmodels.StartProcessUtil - com.appiancorp.kougar.driver.exceptions.Signal: At least one referenced Activity Class Schema is invalid: ,230
07:00:38,838 INFO [stdout] (http-0.0.0.0:8443-8) com.appiancorp.kougar.driver.exceptions.Signal: At least one referenced Activity Class Schema is invalid: ,230
07:00:38,838 INFO [stdout] (http-0.0.0.0:8443-8) at com.appiancorp.kougar.driver.ipc.IpcConnection.get(IpcConnection.java:390)
07:00:38,838 INFO [stdout] (http-0.0.0.0:8443-8) at com.appiancorp.kougar.driver.ipc.IpcConnection.call(IpcConnection.java:840)
07:00:38,839 INFO [stdout] (http-0.0.0.0:8443-8) at com.appiancorp.kougar.driver.ipc.IpcConnection.call(IpcConnection.java:821)
07:00:38,839 INFO [stdout] (http-0.0.0.0:8443-8) at com.appiancorp.kougar.driver.KougarConnection.call(KougarConnection.java:336)
.....

 someone knows why

thank you very much!